Culture of brain tumor patient peripheral blood lymphocytes (PBL) with recombinant Interleukin-2 (rIL-2) results in the activation of lymphokine activated killer LAK cells capable of killing brain tumor cells. PBL obtained from brain tumor patients by constant flow cell separators were cultured with IL-2 for three to five days. Cells were tested for their ability to lyse fresh tumor targets. These LAK cells were infused with IL-2 into patients brain tumor cavities, via a previously placed reservior and cell infusion system. This reservior system was also used to draw specimens of cells and fluid to test for IL-2, evaluate surviving cell number, and LAK activities. Serial CT scans were used to assess the patients response to treatment. Brain tumor patient's PBL were cultured with IL-2 lysed fresh tumor targets. LAK cells and IL-2 infusions were tolerated in brain tumor patients, but with toxicities, transient or permanent, related to the site of treatment. Six patients received 9 treatments; high levels of IL-2 were found in the cyst fluid during treatment. Cell number and LAK activity decreased with time in the cyst. Radiologic evidence of tumor regression was seen in one of five patients evaluated to date. In addition, by performing lumbar drainage with a small lumbar subarachnoid catheter, we study the kinetics of IL-2 in the CSF, and determine the penetration of IL-2/LAK into the CSF and investigate if there is any effect on the blood-brain barrier. In addition, by performing lumbar drainage with a small lumbar subarachnoid catheter, we study the kinetics of IL-2 in the CSF, and determine the penetration of IL-2/LAK into the CSF and investigate if there is any effect on the blood-brain barrier.